In a heavy load tire for example, generally, its tread outline shape a is formed into a single arc shape in a vulcanizing metal mold as simply shown in FIG. 6.
In such a tire, however, in a standard internal pressure state in which the tire is assembled into a rim and a standard internal pressure is charged into the tire, there is a tendency that a tread surface swells radially outward in a region y which is separated from a tire equator by a distance of 0.5 to 0.7 times of a tread half width. For this reason, a difference in circumferential lengths between a swelling portion b and a tread grounding end e is increased, slip between the tread surface on the side of the tread grounding end and a road surface is generated, and uneven wear such as so-called shoulder wear is prone to be generated.
On the other hand, in order to restrain the shoulder wear, Japanese Patent Application Laid-open No. H7-164823 and the like disclose a technique in which the outline of the tread in the vulcanizing metal mold is formed into a double radius shape in which a portion of the tread on the side of the tread grounding end is an arc having a greater radius of curvature than a portion of the tread on the side of the tire equator, thereby bringing the outline of the tread in the standard internal pressure state closer to the single arc to restrain the shoulder portion decrease wearing.
Such a technique can restrain the shoulder portion decrease wearing in some degree but there is a problem that new uneven wear is produced in the region y. Especially when a circumferential groove is formed in the region y, uneven wears are seriously generated in inside and outside of the circumferential groove in the axial direction of the tire.
Thereupon, it is an object of the present invention to provide a pneumatic tire in which the uneven wear from the tire equator to the tread edge is restrained and the wear resistance is enhanced.